An 82-year-old man undergoes hip replacement surgery. On the second post-operative night, he becomes confused, agitated, and believes nurses are trying to harm him. He has fluctuating consciousness and picks at his IV line. The next morning he is lucid and cooperative. What feature best distinguishes delirium from dementia?
- A Presence of visual hallucinations
- B Acute onset and fluctuating course of cognitive changes ✓
- C Advanced age of the patient
- D Disorientation to place
Correct answer: B. Acute onset and fluctuating course of cognitive changes
Explanation
The cardinal distinguishing feature of delirium is its acute onset over hours to days with a characteristic fluctuating course, meaning lucid intervals alternating with confusion. Dementia has an insidious onset and a generally progressive course without fluctuation. Although both can involve hallucinations and disorientation, these features are shared. Identifying the abrupt onset and fluctuation is the most reliable bedside distinguishing criterion and forms the basis of diagnostic tools such as the Confusion Assessment Method (CAM).
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.